The invention is based on a hydraulic brake system with an anti-skid system (ABS) and traction control (ASR) for motor vehicles.
In a known brake system of this type, which is embodied as a dual-circuit brake system with front/rear axle or front/rear brake circuit distribution (German Offenlegungsschrift 38 16 073, now U.S. Pat. No. 4,900,102), the reversing valve is embodied as a 3/2-way magnet valve with spring restoration in the connecting line between the master brake cylinder and the hydraulic unit; in its unexcited basic position, it keeps the connecting line open and thus connects not only the control valves assigned to the wheel brake cylinders of the driven wheels, but also the outlet of the operative pump element in the brake circuit of the driven wheels, to the master brake cylinder, while in its reversed position brought about in traction control, it disconnects the connecting line and connects the outlet of the pump element to the brake fluid tank, via a series circuit of two pressure limiting valves. The reversing valve is controlled by the electronic control system and is switched over whenever at least one of the driven wheels is exhibiting slip. At the same time, the return pump is switched on. The operative pump element in the brake circuit of the driven wheels, which is embodied as self-aspirating, aspirates brake fluid from the brake fluid tank via the charge valve and produces a brake supply pressure that is fed via the control valves into the wheel brake cylinders of the driven wheel or wheels that are slipping. Excess brake fluid is returned to the brake fluid tank via the reversing valve and the pressure limiting valves.